This invention pertains to a primer composition for adhering the silicone rubber, especially the so-called addition-type silicone rubber that cures by the reaction of the vinyl group directly bonded to the silicon atom with the .tbd.Si--H linkage, with plastics, metals, and especially polyvinylchloride resin.
This addition-type silicone rubber is composed of polyorganosiloxane holding at least two vinyl groups in a molecule, polyorganosiloxane holding at least two .tbd.Si--H bonds in a molecule and platinum catalyst. It is cured by addition reaction of vinyl groups and Si--H bonds at a temperature from room temperature to approximately 200.degree. C. This kind of silicone rubber is usually cured at 100.degree. C. to 150.degree. C. for a few minutes. Therefore, it is widely used for encapsulation material and molding material for electronic elements and electric and electronic components.
In particular, this silicone rubber, when compounded with filler or pigment, is so good in flame retardation that it is widely used for encapsulation of flyback transformers of televisions and molding materials for voltage multipliers of televisions.
This kind of addition-type silicone rubber, has the shortcoming that it is poor in adhesive properties with plastic and other materials; therefore, its use is limited. In order to solve this problem, various primer compositions were devised. But it is extremely difficult to provide satisfactory adhesive property for both plastics and metals, and thereby applications for electric and electronic components using a variety of materials are limited.
There was discovered a primer composition which provides addition-type silicone rubbers with excellent adhesiveness to many kinds of plastics and metals by blending tetetraorganotitanate possessing an organic group with two to eight carbon atoms or its polymerized compound, an epoxy-group-containing organosilicon compound, an unsaturated-bond-containing organosilicon compound, platinum or its compounds, an organic polymer soluble in an organic solvent, and one or a combination of more than two kinds of organic solvents. Such a composition is disclosed in Japanese Patent Application 1978, No. 107757--referring to Patent announcement 1977-32030.
That invention opened the way for using addition-type silicone as an encapsulation and molding material for electric and electronic components. However, one of the problems with such primer composition was it had poor adhesive property with polyvinylchloride type resins, particularly with semi-hard polyvinylchloride coated electric wire used as lead wire. Thus, its use with some electric and electronic components is limited.
Accordingly, there is presented by the present composition a primer composition that provides a satisfactory adhesive property of addition-type silicone rubber with polyvinyl chloride type resin without detracting the adhesive properties with other plastics and metals.